Ignition of electric arc discharge devices



Feb. 14, 1967 w. HENDEL ET AL 3,304,465

IGNITION OF ELECTRIC ARC DISCHARGE DEVICES Filed June 25, 1962 PULSE GENERATOR INVENTORS, HANS w. HENDEL a ROBERT a. LAUTTMAN.

ATTORNEY.

United States Patent Ofilice 3,304,465 IGNITION F ELECTRIC ARC DISCHARGE DEVICES Hans W. Hendel, Manasquan, and Robert G. Lauttman, Neptune, N J assignors to the United States of America as represented by the Secretary of the Army Filed June 25, 1962, Ser. No. 205,137 4 Claims. (Cl. 315330) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

The present invention relates to arc discharge devices, and more particularly to a novel means for causing breakdown in gas discharge tubes of the arc type.

In order to ignite or strike an arc in a gaseous atmosphere in which an electric field exists, it is necessary to cause ionization and breakdown of the gas. Once breakdown is achieved, the arc becomes self-sustaining and becomes an efficient conductor of electricity. After breakdown most of the interelectrode space is occupied by an electrically neutral plasma composed of electrons and ions. The action of the applied electric field draws electrons from the plasma toward the anode or positive elec trode and draws positive ions toward the cathode or negative electrode. The anode electrons constitute the load current supplied to the external circuit. The electrons and ions thereby lost by the plasma are continually replenished by electrons supplied by the cathode and from ionization resulting from electron-molecule and ionmolecule collisions. In prior art devices several different means have been utilized to ignite the are or initiate breakdown. In hot-cathode arc tubes of the thyratron type, grids are usually used for this purpose, however externally produced magnetic fields and auxiliary glow discharges have also been used to produce breakdown. In mercury pool type tubes an ignitor rod immersed in the mercury cathode is used to strike the arc. The present invention provides a novel and advantageous means for causing rapid and controllable breakdown of arc tubes.

Briefly stated, the present invention comprises an arc discharge device in which breakdown is accomplished by projecting a plasma cloud into the gaseous atmosphere of the interelectrode space.

It is therefore an object of this invention to provide novel and improved means for striking arcs in gas discharge devices.

It is a further object of this invention to provide means by which the breakdown time of arc discharge devices may be adjusted by changing the orientation of the elements within the device.

It is a further object of this invention to provide an arc discharge device capable of supporting extremely heavy load currents immediately following breakdown.

Other objects and advantages will become apparent from the following detailed description and drawing, in which the sole figure of the drawing is a schematic representation of a preferred embodiment of the invention.

The drawing illustrates the invention as applied to a mercury cathode type arc discharge device. The tube envelope 17 contains a mercury pool 5 in contact with a cathode electrode 6 which is connected to a source of negative potential. The anode 3 is connected to the positive terminal of the same potential source via anode lead 4. Mounted in the tube wall is plasma gun 12 adapted to project a plasma into the tube and thereby cause avalanche formation and breakdown between the anode and cathode. Plasma gun 12 comprises a body of dielectric material 11 in which are embedded two closely spaced metallic electrodes 13 and 14. The electrodes are connected via leads 7 and 9 to a pulse generator .15.

3,304,465 Patented Feb. 14, 1967 When ignition of the tube is desired a high voltage pulse with an amplitude of several kilovolts and a rise time of the order of 10 seconds is applied to the electrodes 13 and 14 by the pulse generator. This high voltage causes arc-over between the exposed ends of electrodes 13 and 14, vaporizing and ionizing some of the electrode material. The plasma produced in this manner expands rapidly throughout the tube interior. The large number of electrons present in the plasma results in high probability of collisions with the neutral mercury atoms within the tube and leads to rapid ionization of the mercury vapor. The plasma produced by the interaction of the gun plasma and the mercury vapor is capable of sup porting heavy peak currents. This feature is advantageous, for example, in radar modulators, wherein such a tube could be used to rapidly discharge a pulse forming network in order to .generate a pulse for application to a magnetron tube. In elfect the plasma gun 12 sup plies a ready-made plasma which can support heavy load currents pending the formation of the steady-state plasma which is composed of mercury ions and electrons.

Depending on the positioning of the plasma gun, ionization times between 3X10 and 10- seconds have been achieved with the illustrated device in laboratory tests. If the gun is arranged to project the plasma toward the anode, the initial velocity of the electrons in the plasma will be supplemented by the accelerating force of the applied electric field and the ionization time will be short. If projected toward the cathode, the plasma electrons will be decelerated, resulting in slightly longer ionization time. A further advantage of the disclosed device is that the plasma gun need not'be electrically or physically connected to either the anode or cathode, however it can be connected to either of these two electrodes, depending on the ionization time required and the requirements of the external circuitry. The device therefore allows for more flexible circuit arrangements than is possible with an ignitron, for example, in which the ignitor rod must be immersed in the liquid cathode.

The practice of the invention need not be limited to the illustrated structure. Any convenient and practical means may be used to form and project the plasma into the tube. The illustrated plasma gun is known per se and is described in an article in the Physical Review, vol. 104, No. 2, Oct. 15, 1956, pp. 292299, entitled Experimental Study of Ionized Matter Projected Across a Magnetic Field, authored by Winston H. Bostick.

Accordingly, the invention should be limited only by the scope of the appended claims.

What is claimed is:

.1. A mercury arc tube comprising; an envelope, a mercury pool cathode, an anode, means to apply a positive voltage to said anode and a negative voltage to said cathode, a pair of closely spaced metallic electrodes embedded in dielectric material, said dielectric material being mounted in said envelope intermediate said anode and cathode, and means to apply a high voltage pulse to said electrodes, thereby projecting a plasma into said tube and causing rapid ionization of the mercury vapor therein.

2. In an arc discharge tube of the type including an anode and a mercury pool cathode sealed in a gas-tight envelope, the improvement comprising; a pair of closely spaced metallic electrodes mounted within said envelope and means to cause arc-over between said metallic electrodes whereby portions of said electrodes are vaporized and ionized, thereby projecting a plasma into said envelope and rapidly causing ionization of the mercury vapor within said tube.

3. In an arc discharge tube of the type including an anode, cathode and an ionizable gas sealed in a gas-tight envelope, the improvement comprising; a pair of closely spaced metallic electrodes mounted within said envelope,

J 4 and means to cause arc-over between said metallic elec- References Cited by the Examiner trodes whereby portions of said electrodes are vaporized UNITED STATES PATENTS and ionized, thereby projecting a plasma into said envelope and rapidly causing ionization of said .gas. 1,697,281 1/1929 Meyer 315*168 X 4. An are discharge tube comprising, an anode, a 5 19801459 11/1934 whlte 315168 cathode and an ionizable gas sealed in a gas-tight enve- 2,367,556 1/1945 Arno 313 170 lope, a pair of closely spaced metallic electrodes mounted 2,921,236 1/1960 Gawehn 313M197 3,248,603 4/1966 Howell Ct 211. 313198 within said envelope, means to apply a high voltage pulse to said electrodes thereby vaporizing and ionizing portions of said electrodes and rapidly causing ionization of 10 the gas within said tube.

DAVID J. GALVIN, Primary Examiner. 

3. IN AN ARC DISCHARGE TUBE OF THE TYPE INCLUDING AN ANODE, CATHODE AND AN IONIZABLE GAS SEALED IN A GAS-TIGHT ENVELOPE, THE IMPROVEMENT COMPRISING; A PAIR OF CLOSELY SPACED METALLIC ELECTRODES MOUNTED WITHIN SAID ENVELOPE, AND MEANS TO CAUSE ARC-OVER BETWEEN SAID METALLIC ELECTRODES WHEREBY PORTIONS OF SAID ELECTRODES ARE VAPORIZED AND IONIZED, THEREBY PROJECTING A PLASMA INTO SAID ENVELOPE AND RAPIDLY CAUSING IONIZATION OF SAID GAS. 